The Transition from Wakefulness to Sleep Is Marked by a Progressive Loss of Consciousness, Reduction of Stimulus Reception, Cessation of Behavioral Response, and an Absence of Memory.1

THE TRANSITION FROM WAKEFULNESS TO SLEEP IS MARKED BY A PROGRESSIVE LOSS OF CONSCIOUSNESS, REDUCTION OF STIMULUS RECEPTION, CESSATION OF BEHAVIORAL RESPONSE, AND AN ABSENCE OF MEMORY.1 Accordingly, for the sleeper, the exact point of sleep onset is elusive. One interesting finding to emerge from research on human sleep is that many people with insomnia overestimate their sleep-onset latency (SOL) and underestimate their total sleep time (TST), relative to polysomnography.2-9 Further, when woken up from polysomnographically defined Stage 2 sleep, people with insomnia are more likely than good sleepers to report having been awake the moment just before they were woken,10-15 a finding recently replicated by Mercer and colleagues.16 The International Classification of Sleep Disorders, Revised, defines sleep state misperception (also known as pseudoinsomnia or subjective insomnia) as a disorder in which a complaint of insomnia arises when polysomnography demonstrates a “normal sleep pattern” with sleep latencies of less than 15 to 20 minutes, sleep durations in excess of 6.5 hours, and a normal number and duration of awakenings.17p33 However, the utility of this diagnosis has been questioned on the basis that distorted perception of sleep is ubiquitous among people with insomnia.18-19 Indeed, there is evidence that distorted perception of sleep occurs across various diagnoses published in The International Classification of Sleep Disorders, Revised, including psychophysiologic insomnia, insomnia associated with depression, and insomnia associated with inadequate sleep hygiene.6,20 It seems likely then that individuals with sleep state misperception represent only 1 extreme of a continuum.18,21 The role of distorted perception of sleep in the maintenance of insomnia has been increasingly recognized, as reflected in its incorporation into 2 recent theoretical models of chronic insomnia. First, Perlis and colleagues,22-23 based on the observation that people with insomnia exhibit more high-frequency electroencephalographic activity (in the beta to gamma range) at or around sleep onset, have proposed that cortical arousal may account for distorted perception. Cortical arousal is conceived of as 1 of 3 forms of arousal that may contribute to insomnia: cortical, cognitive, and somatic arousal. While the model recognizes that these 3 forms of arousal interact, it is suggested that cortical arousal (as a conditioned response) is the “primary feature of insomnia.”22p185 Second, Harvey24 has proposed that distorted perception of sleep is 1 of the core maintaining processes in chronic insomnia. According to this model, the perception of insufficient sleep increases worry about sleep and anxiety that, in turn, worsens sleep because worry and arousal are antithetical to optimal sleep onset.24 Consistent with this proposal, it has been suggested that distorted perception of sleep, in its severe form, may be considered a “prodromic or transitional state” in the development of objective insomnia.19p908 Despite its potential theoretical and clinical significance, little is known about the mechanisms underpinning distorted perception of sleep in insomnia. One mechanism proposed to underpin distorted perception of sleep in insomnia is cognitive arousal. The majority of individuals with insomnia cite cognitive arousal as the primary determinant of their sleep disturbance.25-26 The presence of cognitive arousal during the presleep period is highly correlated with subjectively estimated and objectively measured SOL.27 Further, a number of laboratory studies have demonstrated that experimentally increasing presleep cognitive arousal, in good sleepers, increases objective SOL.28-30 Taken together, these findings raise the possibility that cognitive arousal is a cause, rather than a by-product, of sleep disturbances. Further, based on the robust finding from the timeperception literature that time seems longer when the number of units of information processed per unit of time increases,31-33 it has been proposed that cognitive arousal during the presleep period may be the cause